Background: I'm playing on Very Hard (old Survival), and wanted to try a permadeath, no-health run.

I have noticed a non-deterministic health bar regeneration in Fallout 4, but I cannot pinpoint where it comes from. I just eventually notice that health is back when it shouldn't be. Also, any accumulated rads seem to disappear, and HP appears to go to max.

I installed a mod to stop health regen when levelling up (as well as other assorted texture packs and radio stations which shouldn't affect health). But this regen is not tied to level ups it seems to happen whenever I don't closely watch the health bar. Obviously, I didn't add any mods or perks that regen health.

As far as I understand it the game does not have a default regen-over-time mechanic for health.

What mods do you have installed? This definitely does not sound like normal behavior in game without a corresponding perk, but it is possible having multiple mods interacting with each-other could explain this phenomenon. I would also check your equipment, I believe there are some legendary items that might also have passive healing effects.
– onewhoAug 2 '18 at 13:27

1

"This mod will remove the passive health regeneration bonus from Lifegiver level 3 and the Astoundingly Awesome magazine." - You're on survival difficulty, right? And also starving yourself? And not drinking anything? ... Yeah, this isn't going to work. You need a mod that removes the 'survival' from survivor difficulty, or just play in only hard mode.
– MazuraAug 3 '18 at 23:48

There is a bug in Fallout 4 survival mode, where when you go to sleep while affected by an active effect from a consumable (other than satisfying thirst/hunger), that effect stays indefinitely after you wake up. You will be notified that the consumable has worn off and the effect will not be shown as "active effects" in the Pip-boy. However the effect itself can be seen in the Pip-boy.

For example, I once had a permanent 25 radiation resistance after consuming vegetable soup, with no detectable source (perks, gear, active effects). I don't know if this bug still exists (if it was patched or not) or how consistently it works and with which consumable it works.
Health regen is for example granted by deathclaw omelettes.

I made a Fallout 4 mod for that very purpose, called "You Only Live Once" mod by Nuigurumi, available the usual way, through the in-game "Mods" menu. It tracks your received damage (including limb damage) and radiation and doesn't let them decrease, thus removing any healing. You can eat/drink/sleep in new Survival, use stimpaks if you want, take Lifegiver, etc. - they may have their appropriate other effects, just won't restore your health or remove radiation. Well, as far as I have tested. As usual, I can't guarantee it won't screw you up at some point in game. Worked for me, though.

Yes, I actually say your mod and tried it at some point. But it didn't work for me. Every time I leveled up, it detracted more and more HP. I'm not sure if it was acting up against some perk or if it was because I activated it at a later point in the game. But it almost killed me :)
– bitmaskSep 7 '18 at 6:04

@bitmask Sad. I myself lost a couple of characters to it, because I thought I had debugged it enough and it's time to play, but it wasn't, and it started giving me some damage every time I slept. I fixed that, broke something else in the process - it started breaking my legs, like, every second or third time I slept. I fixed that, then completed an entire play-through without a single problem. But even when it wasn't well debugged yet, I never experienced problems on level ups. Activating it later in the game shouldn't be a problem. What were your build and perks at the time?
– HeadcrabSep 7 '18 at 7:26

I don't remember the build exactly. I think it was medium END, low STR no LCK.
– bitmaskSep 7 '18 at 12:28